Electronic timing circuit



Dec. 13, 1960 i P. c. BROCKETT' 2,964,625

ELECTRONIC TIMING amour:

Filed Aug. 15, 1957 2 Sheets-Sheet 1 Guam... M

Fig. 1

INVENTOR. PETER C. BROCKETT BY 61mm 8w. ATTORNEY Dec. 13,1960

Filed Aug. 15, 1957 EIL llb

INVENTOR. PETER -C. BROCKETT.

6221a: ATTORNEY.

United States Patent ELECTRONIC TIMING CIRCUIT Peter C. Brockett, Milford, Conu., assignor to Eastern Industries, Incorporated, East Norwalk, Conn., a corporation of Delaware Filed Aug. 13, 1957, Ser. No. 677,993

20 Claims. (Cl. 328-169) This invention relates to electronic circuits and more particularly to an improved electronic timing circuit utilizing thermionic vacuum tubes for the precise control of timed intervals of controlled devices.

This timing circuit is adjustable by manual means, so that the controlled interval may be pre-set, as desired, over a wide timing range within the limits of the circuit elements. The circuit also is adapted for quick or controlled reset at the end of the time interval or during the time interval as desired. Reset during the time interval may be employed to prolong or extend the time interval as by traffic actuation for example.

The invention is an improved electronic timing circuit which can be made to activate or energize a trigger or relay at a preset interval of time after the timing circuit is set into operation. The time interval is controlled by certain passive circuit elements, the use of which results in a constant time interval. even though there may be some variations in characteristics of the tubes used in the circuit or in the voltage of the power supply for the circuit. The end of the timing period is clearly defined by a sudden change in plate current in an electronic tube at a predetermined desired voltage level in a control circuit whose voltage varies progressively in timing.

The improved timing circuit is designed for standard stock vacuum tubes such as one dual triode type tube or two single triode type tubes.

It is an object of the present invention to provide an improved timing circuit capable of manual adjustment of timing for providing a triggering action or other distinct change in output at the end of a precisely timed period, for controlling a work circuit or device.

Another object of the present invention is to provide a timing circuit employing vacuum tubes of a readily available type, and to utilize the tubes in such a manner as to provide an inherently stable timing characteristic which is substantially independent of normal variations in operating characteristics between individual tubes of suitable type or over their operating life.

A still further objector this invention ,is to obtain a sudden large change of energy output at the end of a pro-determined .intervalof time to actuate arelay or other control device clearly, without chattering, and despite possible wide variation inoperating characteristics of such relay orcontrol device,.as mayoccur between different commercial relays or by wear over the lifetime of any one relay.

Another object of the present invention is to provide an electronic timing circuithavingsnocappreciable change intiming even though there is .a wide variation of supply voltage. I

It ,is an ,additional object. of .the invention ,to present an improved timing circuit that utilizes the characteristics ofpassive circuit elements to control the timing interval.

Fig. 1 shows one form of timing circuit inaccordance with theinvention.

Fig. .2,shows another-form of timingcircuit according to the invention but having a somewhat difiierent output and employing electronic reset of the timing.

Referring now to Fig. 1, one embodiment of the electronic timing circuit according to the invention is illustrated in schematic form and in association with an electromagnetic device and ratchet mechanism controlled by the timing circuit, such ratchet mechanism being shown in the lower right part of Fig. l. The circuit along the right side of Fig. 1 is presented to illustrate one of the methods of resetting the timing circuit, and the ratchet mechanism is presented to show one of the many possible uses or work devices with which the timing circuit may be employed.

Fig. 2 illustrates another form of electronic timing circuit according to a further aspect of the invention, this form employing the same principle as is employed by the electronic timing circuit as shown in Fig. l to obtain a precise time interval, but differing in some respects in its output and in that the reset circuit is electronic rather than electro-mechanical.

The circuit of Fig. 2 employs an electronic reset device generally known as a one shot multivibrator rather than a relay operated mechanical reset switch for example. Another difference is the manner in which the energy is used. Fig. 2 develops two output voltage pulses of opposite polarity that are simultaneously obtained at the end of the time interval, either of which pulses are available for external use by appropriate connection, while the output developed in the circuit of Fig. l at the end of the time interval is a surge of current and consequent operation of a relay.

The circuit of Fig. 1 illustrates two forms of the invention, depending on the position of the switch 83, the first preferred form with the switch on contact as shown employing the slow charging of the timing capacitor 16 for timing and its quick discharge for reset of the timing action, and the second form with switch 83 moved to its alternate contact 87 employing the slow discharge of capacitor 16 for timing and its quick recharging for reset, as more fully described below.

Considering the circuit of Fig. 1 in more detail, with switch 83 connecting contacts 84 and 85 as shown, the timing circuit operates from a direct current source between positive and ground at the left side of the drawing. A voltage divider circuit comprising resistor 8, potentiometer 10 and resistor 11 in series is connected across the DC. source between positive at line 9 and ground at line 12. A charging circuit for timing capacitor 16 extends from tap 13 on the potentiometer 10 via junction 89, resistor 14, tap 15, line 75 and capacitor 16, returning via contact 84, switch 83 and line 86 and the ground line 12. This charging circuit includes adjustable taps 13 and 15, so that the amount of voltage tapped off the voltage divider and the current flow through resistor 14 via tap 15 may be selected and controlled to charge capacitor 16 at a desired timing rate.

A discharge circuit for capacitor 16 includes resistor 17 and switch or contact 18, and is connected between the input side of capacitor 16 and ground line 12, the resistance 17 being of low value to provide a substantially complete discharge of the capacitor 16 when contact 18 is closed.

A second voltage divider, completed from the DC. input 9 through the coil of relay 19, resistor 20, potentiometer 24 and resistor 21 to ground line 12, is used to obtain a desired potential on grid 22 of tube 23 by joining grid 22 to the potentiometer 24 at point 24'. The plate 25 of tube 23 is joined to the DC. input 9 by a connection of a low impedance.

Cathode 26 of tube 23 and cathode 27 of tube 28 are interconnected and are then connected to ground line 12 through resistor29, while capacitor 311 forms a parallel circuit from the joined cathodes 26 and 27 to the ground line 12. The plate 31 of tube 28 is joined via line 91 to the second voltage divider circuit at point 32, while the grid 33 of tube 28 is joined to the input side of the capacitor 16 so that the potential of this grid is controlled and determined by the amount of change on the capacitor 16.

Resistor 34 and by-pass tap 35 serve for current control in the circuit of grid 33 as described more fully below.

The vacuum tubes used in the circuit may be either a pair of triode type tubes or one dual triode type tube as shown, or may be of any other suitable type such as tetrodes or pentodes having sharp cut-off characteristics.

The circuit made up of power supply 37, contact 36 controlled by relay 19, and relay or electromagnet 38 is used to illustrate a means of closing reset contact '18 at the end of the timed interval and also for operating some other device, as for example the ratchet assembly consisting of an arm and pawl 39 and the ratchet wheel 48. The relay or electromagnet 38 is designed to attact the arm and pawl 39 of the ratchet assembly to the left to engage the next tooth of ratchet wheel 48 before contact 18 is closed to complete the discharge circuit. The ratchet wheel is then advanced by the return spring 49 when electromagnet 38 is deenergized by the release of relay 19 by the reset of the timing circuit. The pawl 47 prevents reverse rotation of ratchet wheel 48 in the usual manner. The ratchet wheel may actuate a step-by-step cyclic switch or counter or other control or utilization device not shown.

With reference to the operation of the timing circuit in Fig. 1, let us first assume that contact 18 is closed completing the discharge circuit to discharge capacitor 16 through resistor 17 and contact 18 to the ground line 12. With the contact 18 closed the capacitor 16 is also prevented from charging by the shunting of capacitor '16 by the low resistance of 17. The completion of this discharge circuit reduces the voltage across the capacitor 16 to substantially zero and thus the potential on the grid 33 is also at zero or ground and keeps the tube 28 non-conducting since the grid is at high negative bias with respect to cathode 27 by the voltage across resistance 29 as described below.

Tube 23 is now passing current from the DC. input 9 via line 95, plate 25, cathode 26, through resistor 29 to the ground line 12. The passage of current through tube 23 is controlled by the potential on grid 22 from the voltage divider at point 24'.

Since cathodes 26 and 27 are interconnected, both will have the same cathode voltage, which will be above ground i.e. positive with respect to ground 12 because of the voltage developed across resistor 29 by this current through it. Thus grid 33 of tube 28 will be negative biased beyond cut-off with respect to cathode 27 and tube 28 will be non-conducting, but grid 22 of tube 23 will be at low or near zero bias with respect to its associated cathode 26 by reason of the current fiow in the potential divider including the coil of relay 19 and the resistors 28, 24 and 21 in series, thus keeping tube 23 conducting in this initial condition.

The flow of current through the voltage divider from DC. input 9 through relay 19, resistors 20, 24 and 21, to ground line 12 is not sufiicient to energize the relay 19 in this condition, and the relay 19 releases and opens its contact 36 which in turn releases electromagnet or relay 38 so that the latters contact 18 opens and breaks the discharge circuit.

The timing action now starts as the capacitor 16 begins to charge from D.C. input 9, through resistor 8, potentiometer 18, taps 13 (selecting the amount of voltage desired), resistor 14, tap 15 (controlling the amount of current flow), lead 75 to capacitor 16 which is connected via switch 83 and lead 86 to ground line, 12.

As the charge on capacitor 16 is increased, the poten tial on grid 33 becomes more positive with respect to ground and thus less negative with respect to cathode 27. Therefore, at a pre-determined time after the opening of switch 18, as determined by the setting of tap 15, the negative bias of grid 33 is reduced below cut-off allowing tube 28 to start conducting. When tube 28 starts to pass current, the current is drawn from point 32 through relay coil 19. Since relay coil 19 is part of the voltage divider 19, 20, 24, 21, this current through the coil increases materially the potential difference across the coil and thus reduces the potential across the remainder of the potential divider and therefore reduces the potential as applied to grid 22.

With a reduced potential on grid 22, the current flow through tube 23 is reduced thereby reducing the cathode voltage on both cathodes 26 and 27. With a reduced cathode voltage on cathode 27, tube 28 increases its flow of current from the plate 31 to the cathode 27 thereby drawing more current from point 32 and amplifying the entire reduction and amplification actions of the two tubes. This reduction and amplification is very rapid and, as the current flow is increased through tube 28, the rapid increase of current flow from the DC. input 9 through the relay 19 to point 32 and via line 91 to tube 28, through resistor 29, to ground line 12 energizes relay 19.

Relay 19 attracts and closes contact 36 completing a circuit from the power supply 37 through the coil of relay 38. Relay 38 is energized and attracts the arm and pawl 39 of the ratchet assembly and causes the pawl to notch into thenext position of the ratchet wheel 48. Relay 38 also attracts and closes contact 18 completing the discharge circuit to ground 12.

As the charge on capacitor 16 is reduced, the positive potential on grid 33 (with respect to ground line 12) is likewise reduced increasing its negative bias with re spect to the cathode, and the tube 28 ceases to pass current. The plate 31 does not draw any current from point 32 and the potentials in the voltage divider at points 32 and 24' return to normal. The potential on grid 22 is increased and tube 23 once more passes current as aforesaid. Thus the conduction and non-conduction conditions of the tubes are restored to the initial condition, the relay 19 is deenergized and contact 36 is released and opened. With contact 36 open, the circuit to relay 38 is broken and relay 38 is deenergized and opening contact 18. As relay 38 is deenergized, the arm and pawl 39 of the ratchet assembly is released and the ratchet wheel 48 is advanced as the arm and pawl 39 are pulled back into normal position by the spring 49.

Resistor 34 and by-pass tap 35 in the circuit of grid 33 serve to illustrate alternate forms of control of the circuit at the end of the timing period, particularly as to self-resetting or non-resetting of the timing if the closing of contact 18 fails or is deferred for delayed control purposes for example. If, for example, resistor 34 is bypassed by tap 35, or is eliminated from the circuit entirely, and contact 18 fails to close properly at the end of the timing period in the operation of the timing circuit, the capacitor 16 would not be discharged in the normal manner but would be partially discharged by grid current and the timing circuit would operate as a multivibrator and pulse relay 19 at shortened time intervals. This would be a safety feature in event of temporary blocking of contact 18 by a piece of dust for example. If, however, resistor 34 is inserted into the grid circuit and the contact 18 fails to close properly, the timing circuit will not pulse but rather will maintain a flow of current through tube 28 to keep relay 19 energized. This form of operation would have value in case it is desired to maintain the output condition of the end of the time period, i.e. with relay 19 operated, for any considerable time before reset contact is closed. The amount of resistanee :in theugrid circuit can thus be selected or adjusted for the desired action.

In the foregoing description it was assumed that contact 18 was controlled by relay 38 which relay was in a second circuit, the second circuit being controlled by relay 19 by closure of contact 36 upon relay 19 being energized.

It may be desired to have the electronic-timing circuit reset itself more directly, without the intermediate step of the electromagnetic or work device 38. This could be accomplished by controlling contact 18 directly by relay 19 for example. This would eliminate thesecond circuit shown in the diagram. The action of the circuit would be the same as previously described except that when relay 19 is energized it would attract and close contact 18 and thus discharge the timing capacitor 16. For this purpose the relay 19 could be of delayed action type if desired. With capacitor 16 discharged the current through relay 19 would be reduced to the point of deenergizing relay 19 so that contact 18 would be released and open causing a break in the discharge circuit and capacitor 16 will begin recharging again.

The circuit presented in Fig. 1 may be set-up with the following typical circuit element values, which are given as an example but without limitation of the invention thereto. The current supply line 9 may be at 175 volts direct current with ground line 12 at zero for example. This direct current may be derived by rectification of an alternating current supply, not shown, for example. The input voltage divider resistance 8 may be about 2,000 ohms, potentiometer about 15,000 ohms, and resistance 11 may be 39,000 ohms.

Resistor 14 is adjustable at 200,000 ohms per second to charge timing capacitor 16 which has a value of 5 microfarads. The resistance of discharge resistor 17 may be 300 ohms while the cathode resistor 29 may have a value of 16,000 ohms. The capacitor 30 may be of .47 mfd. The voltage divider resistors 20 and 21 may have a value of 100,000 ohms and 180,000 ohms respectively while the potentiometer 24 may have a value of 150,000 ohms resistance. The relay coil 19 may have approximately 10,000 ohms resistance.

If resistor 34 is used, the suggested value of such a resistor is one megohm. The tube may be of dual triode type 12AU7. With a typical timing circuit having the above component values, the potential on grid 22 during timing, i.e. before the end of timing, will be approximately 105 volts while the cathode voltage will be approximately 110 volts. The voltage divider comprising relay l9 and resistors 20, 24, 21 thus provides a voltage at point 24 at approximately 62% of the input voltage at tap 13. This holds the potential of grid 22 at 62% of the input voltage during the timing and establishes the operating point for the triggering action at the end of the timing. It will be found that the value of the timing capacitor 16 multiplied by the value of the working section of resistor 14 will resultin a figureequivalent to the interval of time, in seconds, that is required for the action of the timing circuit from the opening of switch 18 to the energizing of relay 19. The potential divider or potentiometer '10 is adjustable at tap 13 to select the desired input voltage for the capacitor charging timing action, to allow and compensate for normal changes in component values due to manufacturing tolertimes of the circuit elements. The voltage at tap 13 may be the same as the voltage on line 9 but preferably a few volts lower as 165 volts for example .for flexibility in such adjustment.

Resistor :14 is adjustable at tap so'that the value of the ,activesection of resistor 14 may be changed to change the-flowof current and thereby change the timing interval by controlling the charging rate of capacitorj16.

The normal flow of current through relay 19, as a result of the bleeder action of resistors 20, 24 and 21, is not sufiicient to energize relay 19, but relay 19 must be capable of being energized by the flow'of plate current through the tube 28 when the latter becomes conducting to end the time interval. Cathode resistor 29 is usedto establish the voltage on the cathodes 26 and 27 slightly above the operating point for the triggering action of grids 33 and 22. Capacitor 30 acts as a stabilizer to provide a more positive action during changes in cathode voltage in the triggering action. While not essential to operation the inclusion of capacitor 30 improves the operation.

Referring now to Fig. 2 illustrating another form of the invention, certain elements have been identified by the letter a in their reference number to indicate that they correspond in general to those of Fig. 1 having a similar number without the a.

The electronic timing circuit presented in Fig. 2 is arranged for operation from a positive direct current supply, in respect to ground, which is indicated by a plus in a square at the upper left of the schematic in Fig. 2 and a negative direct current supply, in respect to ground, of somewhat less voltage, indicated by a minus in a square at the lower left of the schematic, the ground line 12a, indicated by a circle at the left center being at zero voltage, A resistor 8a, a potentiometer 10a and resistor 11a in series develop the positive direct current supply between plus and ground line 12a, and a resistor 11b is used to develop the negative direct current supply between minus and ground line 12a.

A charging circuit from the direct current supply at tap 13a, on the potentiometer 10a, resistor 14a, tap 15a to the upper side of capacitor 16a, the lower side of which is connected to ground line 12a. Tap 15a is adjustable to control the rate at which timing capacitor 16a is charged, as described heretofore with reference to Fig. 1.

A discharge circuit for timing capacitor 16a is made up of tube 40, a vacuum type triode tube, having plate 41 connected to the upper or input side of capacitor 16a and having cathode 42 connected to the ground side of capacitor 16a through the ground line 12a. Another voltage divider completed from the direct current plus input line 9a through resistor 19a, point 32a, resistor 20a, potentiometer 24a, resistor 21a connected to ground line 12a is used to obtain a potential on grid 22a of tube 23a by connecting grid 22a to the voltage divider at point'24a. The plate 25a of tube 23a is connected to the direct current plus input line 9a through resistor 43. This resistor is used to obtain a positive-going pulse at point 44 when tube 23a becomes non-conducting at the end of the time interval as more fully described below.

The tubes 23a and 2801 are interconnected via their respective cathodes 26a and 27a, the cathodes being connected to ground line 12a through resistor 29a. The plate 31a is connected to the voltage divider circuit at point 32a. Resistor 19a connects point 32a to direct current plus input line 9a and the resistor'19a is used to obtain a negative-going pulse at point 32a when tube 2350. becomes conducting. The grid 33a of tube 28a is connected to the input side of timing capacitor 16a and has an applied potential commensurate with the charge on capacitor V When tube 40 is non-conducting, the timing capacitor 16a is allowed to charge, and thus time an interval. The tube 28a is biased beyond cut-off during the timing interval, and thus the tube 28a is non-conducting'while tube 23a is conducting'in a manner similar to that previously described with reference to Fig. l.

The potential at point 44 is applied to capacitor 46 through line 45, this capacitor serving as a blocking capacitor to prevent steady potential at point 44 from being applied to grid -53 of tube 52, but permitting positive going pulses to'be passed to such grid. Although "capacitor 46 also passes negative going pulses "these are dissipated by diode 70 as described below.

Tube '56 normally passes current through the circuit extending from the direct current negative input line 51 via resistor 57, cathode 55, plate 60, point 63, resistor 61 to ground line 12a. Cathode 55 of tube 56 and cathode 54 of tube 52 are interconnected and thus have the same potential. The grid 53 of tube 52 is at full direct current minus potential via resistor 50, and thus tube 52 is biased normally to cut-off. With tube 52 non-conducting, its plate 65 is substantially at ground potential by reason of its connection via resistor 66 to ground line 12a.

The grid 62 of tube 40 is connected to point 63, from Where grid 62 obtains a grid potential so that tube 40 is biased beyond cut-off to hold tube 40 non-conducting While the tube 56 is conducting.

The grid 67 of the tube 56 is returned through the grid resistor 68 to the ground line 12a, and grid current flows through a circuit extending from the direct current negative input line 51, via resistor 57, cathode 55, grid 67, grid resistor 68 to ground line 12a, keeping grid 67 at approximately the same voltage as the cathode 55 so that the tube 56 normally passes plate current.

The capacitor 69 is connected between the lower ends of resistors 68 and 66 and thus between the grid 67 and the plate 65. and consequently becomes charged when tube 56 is conducting.

At the end of the interval timed as described with reference to Fig. l, the tube 23a becomes non-conducting and a positive-goin pulse is transmitted from pl te 25a of tube 23a to point 44, line 45 through caoacitor 46 to grid 53 of tube 52. to give grid 53 a reduced negative potential. This reduct on in ne ati e potential is enough to overcome the bias on grid 53, as applied from the direct current ne ative input line 51. through resistor 50 to grid 53. and tube 52 passes current through the circu from the direct current ne ative innut line 51. resistor 57. cathode 54. plate 65, resistor 66 to ground line 12a. When tube 52 p sses current the voltage appearing across resi tor 66 shifts the potential at t e ri ht side of capacitor 69 and this caoacitor be ins to discharge through resistor 68. The bias on grid 67 of tube 56 is thus increased so that tube 56 becomes non-conducting.

W en tube 56 is cut-ofl and no plate current is flowing through resistor 61. the grid 62 of tube 40 is returned to ground line 12a through resistor 61 and no bias volta e is applied to grid 62 so that tube 40 will pass current thereby discharging timing capacitor 16a.

The ne ative si nal applied through capacitor 69 to grid 67 of tube 56 holds tube 56 biased to cut-ofi for a period of time as determined bv the value of capacitor 69 and the resistance of resistor 68 and thus controls reset of the timing circuit.

At the termination of this reset time, as determined by the value of capacitor 69, the resistance of resistor 68. tube 56 will again pass current through resistors 57 and 61 when caoacitor 69 becomes sufiiciently discharged, since the positive-going pulse via capacitor 46, which triggered the reversal of conduction conditions by rendering tube 52 conducting, has dissipated. The voltage across resistor 57 will restore tube 52 to its non-conducting state, and the voltage developed across resistor 61 will again bias tube 46 to cut-off and open the discharge circuit of timing capacitor 16a.

The circuit including tubes 52 and 56 thus serves as a one-shot multi-vibrator for controlling discharge of the timing capacitor 16a via tube 40.

Tube 70, a vacuum tyne diode, is used to prevent the trailing edge of the positive-going pulse from the plate 25a through point 44, line 45, capacitor 46 to grid 53 from restoring the one-shot multi-vibrator prematurely to its normal condition. The negative-going trailing edge of the pulse is dissipated via the connection through the cathode 71 and plate 72 of diode 70 to line 51.

At the termination of the time interval, as determined by the amount of time taken to charge timing capacitor 16a as previously described, a positive-going pulse is obtained at point 44 from plate 25a of tube 23a when tube 23a becomes non-conducting. The positive-going pulse may be measured from point 73 to ground line 12a. At the same time, a negative-going pulse is obtained at point 32a as tube 28a passes current. This negativegoing pulse, positive with respect to ground, may be measured from point 74 to ground line 12a.

The positive-going pulse, positive with respect to ground, is used, among other things, to start the multivibrator resetting action as previously described.

Either the positive-going pulse available between point 73 and ground line 12a or the negative-going pulse available between point 74 and the ground line 12a indicate the end of the timed period and either pulse may be used to trigger another electronic switching circuit or other external work device, not shown in Fig. 2.

Resistor 34a and by-pass tap 35a serve purposes similar to those previously described for resistor 34 and tap 35 in the description of Fig. 1.

It will be obvious to those skilled in the art that the timing circuit may be arranged to operate at a lower voltage level, if desired, while the same principle of operation is maintained.

Operation of the timing circuit on a lower voltage level for the triggering of the tubes 23 and 28 at the end of the time interval, as well as for the charging-discharging of the timing capacitor 16, could be accomplished without reducing the direct current supply voltage on line 9, by increasing the impedance of resistor 8 and reducing the impedance of resistor 11, or by setting the tap 13 on the potentiometer 10 nearer ground for example and in either of these cases, by also increasing the impedance of resistor 20 and reducing the impedance of resistor 21, or by setting the tap 24 on the potentiometer 24 nearer ground, for example, accordingly thereby maintaining the voltage at tap 24 approximately at 62% of the voltage at the tap 13, for example. The cathode resistor 29 would also be reduced to maintain the desired plate current for operation of relay 19.

This manner of providing a lower operating level for the charging of the timing capacitor 16 would introduce additional resistance in series with the main adjustable timing resistance 14 and this might require adjustment of calibration of resistance 14 for quite short time intervals to the extent that the total resistance of resistor S and of the working part of potentiometer 10 forms a substantial percentage of the resistance of the working part of the adjustable resistor 14.

The circuit may be operated at a lower voltage level by reducing the voltage of the DC. supply on line 9, without any major readjustment of the voltage dividers, provided that the relay 19 is of sufiicient sensitivity. Some readjustment of the voltage dividers or of cathode resistor 29 or both may be made to accommodate to relay sensitivity as will be obvious to those skilled in the art.

With either method of reducing the voltage operating levels of the circuit, the operating grid potential on the grid 22 would be reduced accordingly during the timing interval with the cathode voltage on cathodes 26 and 27 also being reduced. The potential of grid 33, with respect to ground, necessary to terminate the timing interval by the triggering operation, would be reduced, while the amount of charge on the timing capacitor 16 required for such operation would likewise be reduced.

Operation of the timing circuit at an input supply of the order of to volts DC. for example, will permit the circuit to obtain this direct current supply by rectification of a normal alternating current power supply, without the need of a step-up transformer or other means for increasing the alternating current voltage.

Thus the direct current power supply may be obtained by rectification of an alternating current power supply with smoothing capacitor in well known manner as de- 9 sired, at a low voltage without a voltage step-up device or at higher voltage with s'ucha device.

The one-shot multi-vibrator, illustrated in Fig. 2, that serves to reset the timing circuit via discharge of timing capacitor 16a through tube 40 at the termination of the timed interval, may be one of any of the well-known types of one-shot multi-vibrators.

The timing circuit illustrated in Fig. 2 may be operated at various supply voltages at line 9a and also at a low voltage level for the triggering of the tubes 23a and 28a at the end of the time interval, without reducing the direct current voltage supply on line 9a in a manner similar to that described with reference to Fig. 1 above.

As above described the timing capacitor has been charging relatively slowly during the timing and has been discharged quickly for reset of the timing, this form of operation corresponding to switch 83 connecting points 84 and 85 as shown in Fig. 1.

An alternate method of timing by slow discharge of the timing capacitor and reset by quick charging of this capacitor, may be provided by adjusting switch 83 to its alternate position connecting contact points 84 and '87 and disconnecting point 85.

In this alternate method, the capacitor16 is charged rapidly, when reset contact 18 is closed, this quick charging circuit extending from DC plus, via resistor 8, potentiometer 10, tap 13, point 89, lead 88, point 87, switch 83, point 84 to capacitor 16, returning via line 77, resistor 17, line 78 through closed switch 18 to the ground line 12 return to the DC. source, for reset of timing, and the capacitor 16 slowly discharges for timing via line 75, tap 15, resistor 14, point 89, line 88, point 87, switch 83 and point 84.

In this alternate method of the quick charge reset and slow discharge timing of capacitor 16 the control of the triggering action through grid 33 and all other actions remain the same. However in this alternate method for quick reset a DC. source of low impedance and somewhat greater current producing capacity is required, and resistor 8 should also be of low impedance.

It will be understood line 95 in Fig. 1 may include some impedance such as a resistance of the order of the coil of relay 19 or less for example, as resistance 43 is shown in Fig. 2 for example.

As a further variation of Fig. 1 relay 19 may be replaced by an equivalent resistance above point 32 and relay 19 placed in line 95, with the relay then being normally energized during timing and being deenergized'by the reversal of conduction conditions ending the time interval, and its contacts 36 would be inverted from the normally open form shown to the familiar normally closed form but without any further change in the circuit or its timing and reset action as described in connection with Fig. 1.

Thus several forms or aspects of the invention have beenshown or described, and it will be obvious to those skilled in the art that .variousother changes maybe made 'inthe circuit arrangement orincircuitcomponents without departing from the spirit of the invention.

I claim:

1. A timing circuit for operation from a source of direct current having a positive side and a return side relatively negative with respect to said positive side, including a pair of high vacuum tubes having anode, cathode and control grid and having a common cathode connection of substantial impedance to the return side of said direct current source, connections between the positive side of said direct current source and the respective anodes of said tubes, at least one of said connections including a second substantial impedance in series with the anode, a relatively large impedance connected between said return side and only one anode so connected to said second substantial impedance, the grid of the one of said tubes having the other anode being connected to an intermediate point on said large impedance, a control connection to the '10 grid of the other tube for providing'a bias potential thereon varyingprogressive ly between an initial value and a difierent final value for timing purposes, said other tube being biased to cut-01f and said one tube being at conducting bias at said initial value and during such timing toward said final value and the cut-off and conduction conditions being reversed at said final value, and means for providing an output change responsive to said reversal of conduction conditions whereby external apparatus may be controlled by said timing.

2. A timing circuit as in claim 1 in which said control connection includes a resistance-capacitance circuit for so varying the bias potential on said last named grid by varying the charge on said capacitance.

3. A timing circuit as in claim 1 in which said control connection includes a capacitor connected to control said last named grid, means including an adjustable impedance for charging said capacitor slowly for so varying the potential on said last named grid from said initial value toward said final value for timing, and means for quickly discharging said capacitor for resetting the timing.

4. A timing circuit as in claim 1 in which said control connection includes a capacitor connected to control said last named grid, means including an adjustable impedance for slowly discharging said capacitor for so varying the potential on said last named grid from said initial value toward said final value for timing, and means for quickly charging said capacitor for quickly varying the potential on said last named grid to said initial value for resetting the timing.

5. A timing circuit as in claim 1 in which said control connection includes means for deriving an adjustable voltage from said direct current source for control of the timing.

6. A timing circuitas in claim 1 in which said connection between said large impedance and grid includes means for adjusting the operating potential therefor with respect to such reversal of conduction and non-conduction.

7. A timing circuit as in claim 1 and means controlled by said reversal of conduction conditions at said final Value to restore the grid bias of said other tube toward said initial value to reset said timing.

8. A timing circuit as in claim 1 in which said second substantial impedance includes an electromagnetic device.

9. A timing circuit as in claim 1 in which said second substantial impedance includes a relay.

10. A timing circuit as in claim 1 in which said second substantial impedance includes a relay and which includes means controlled by said relay for resetting said timing.

11. A timing circuit as in claim 1 in which said second substantial impedance includes a relay, and said circuit also including a work device actuated by said relay at the reversal ofsuch conduction conditions at said final value and means actuated by actuation of said work device to restore the grid bias to said initial value to reset the timing.

12. A timingcircuit for operation from a source of direct currenthaving a positive side and a return side relatively negative with respect to said positive side, including a pair of thermionic vacuum tubes having anodes, cathodes and grids, with their cathodes interconnected, resistance and capacitance connected in parallel between said cathodes and the return side of said direct current source, the anode of one said tubes being connected to the positive side of said direct current source, a relay having its coil connected between the anode of the second of said tubes and said positive side, resistance means connected between said last named anode and said return side of said direct current source, the grid of the first named tube being connected to a point on said resistance means to maintain said first tube conducting during timing, a capacitance connected between the grid of said second tube and said return side of the direct current source, a control resistance connected between said positive side and the side of said last named capacitance connected to the last named grid to provide a charge controlling circuit for said last named capacitance for varying the charge on the latter from an initial value to a different final value and for varying the voltage correspondingly between the last named grid and its associated cathode for timing purposes from more negative than cut-off bias initially to substantially less negative than cut-01f bias at the end of the timing period to render said second tube conducting at such end of the timing period, whereby at such end of the timed period the anode-cathode current of said second tube will operate said relay and the consequent voltage drop in said resistance means will bias the grid of said first tube to cut-ofi, and means for resetting said timing by restoring the charge on the timing capacitor substantially to its initial value.

13. A timing circuit as in claim 12 in which said last named resetting means is controlled by said relay.

14. A timing circuit for operation from a source of direct current having a positive side and a side relatively negatively with respect to said positive side, said circuit including a pair of electronic tube units each having an anode and a control grid, and having cathodes interconnected, a substantial impedance connected between said cathodes and said relatively negative side of said direct current source, a relay and a voltage dividing relatively high impedance connected in series across said direct current source, the grid of one of said tube units being connected to an intermediate point on said voltage dividing impedance, the anode of said first tube unit being connected to the positive side of said direct current source and the anode of the second tube being connected between said relay and voltage dividing impedance, a timing capacitor connected between the grid of said second tube unit and one side of the direct current source, and a controlled circuit for varying the charge on said timing capacitor progressively in one sense at a desired timing rate for control of the grid of said second tube unit between cut-off bias and anode-cathode conduction conditions, said first tube unit being conducting and said second tube unit being non-conducting initially during the timing and the conduction conditions being quickly reversed at the end of the timing to operate said relay, and means operated by said relay to reset the timing by varying the charge on said timing capacitor in the opposite sense to restore the initial conduction conditions.

15. A timing circuit as in claim 1 and means including a one-shot multivibrator controlled by said reversal of conduction conditions at said final value to restore the grid bias of said other tube substantially to said initial value to reset said timing.

16. A timing circuit as in claim 1, and an electronic switching circuit controlled by said reversal of conduction conditions at said final value to restore the grid bias of said other tube substantially to said initial value to reset said timing.

17. A timing circuit for operation from a source of direct current having a positive side and a return side relatively negative with respect to said positive side, said circuit including a pair of vacuum tubes having anodes and grids and interconnected cathodes, an impedance connected between the return side of the direct current source and said cathodes, connections between the respective anodes and the positive side of the direct current source and at least one of said last named connections including a further impedance in series with the anode, a relatively large impedance connected between one anode so series connected and said return side of the direct current source, the one of said tubes having the other anode having its grid connected to a point on said large impedance to maintain the said one tube conducting during timing, a capacitor connected between the grid of the other tube and said direct current source, and a control resistance connected between the positive side of the direct current source and the side of said capacitor connected to the last named grid for varying the charge of said capacitor for timing purposes progressively from an initial value to a diiierent final value and for varying the voltage correspondingly between said last named grid and its associated cathode from more negative than cut-off bias initially to substantially less negative than cut-off bias at the end of the timing period to render said other tube conducting at such end of the timing period whereby at such end of the timing period the anode-cathode current of said other tube through the anode connected impedance will provide a substantial change in potential in the latter impedance and will bias said one tube to cut-off by the consequent potential change in said large impedance.

18. A timing circuit as in claim 17 and including means controlled by one of said anode connections responsive to said reversal of conduction conditions for restoring said capacitor and its associated grid substantially to initial value to reset the timing.

19. A timing circuit as in claim 17 and including an electronic switching circuit controlled by one of said anode connections for restoring said capacitor and its associated grid to their respective initial values to reset the timing in response to said reversal of conduction conditions at the end of the timing.

20. A timing circuit as in claim 17, and including a one-shot multi-vibrator circuit connected between said return sde of the DC. source and a second more negative return on said D.C. source and to one of said anode connections to be controlled by the latter to provide a brief control pulse in response to said reversal of conduction conditions at the end of the timing, and an electronic gate circuit controlled by said brief pulse of said multivibrator circuit to restore the charge on said capacitor and the bias on. its associated grid to their respective initial values to reset the timing.

References Cited in the file of this patent UNITED STATES PATENTS 2,519,247 Holden Aug. 15, 1950 2,578,557 King Dec. 11, 1951 2,817,021 Williams et al. Dec. 17, 1957 2,821,628 Purington Jan. 28, 1958 

